Simultaneous view of the FRB~180301 with FAST and NICER during a bursting phase
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2022-03-14
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
FRB180301 is one of the most actively repeating fast radio bursts (FRBs) which has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the magnetosphere
of a highly-magnetized neutron star. We carried out a multi-wavelength campaign with the FAST
radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally
coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19.
We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the
NICER observations. The peak flux-density of the radio bursts ranged between 28 − 105 mJy, the
burst fluence between 27 − 170 mJy-ms, and the burst durations between 1.7 − 12.3 ms. The radio
bursts from FRB 180301 exhibited complex time domain structure, and subpulses were detected in
individual bursts, with no significant circular polarisation. The linear degree of polarisation in L-band
reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in
excess of the background during the 5 ms, 10 ms, 100 ms, 1 sec and 100 sec time intervals at/around
the radio-burst barycenter-corrected arrival times, at a > 5σ confidence level. The 5σ upper limits
on the X-ray a) persistent flux is < 7.64 × 10⁻¹² erg cm⁻² s⁻¹, equivalent to LX < 2.50 × 10⁴⁵ erg s⁻¹ and b) 5 ms fluence is < 2 × 10⁻¹¹ erg cm⁻², at the radio burst regions. Using the 5 ms X-ray fluence upper limit, we can estimate the radio efficiency ηR/X ≡ LRadio/LX−ray & 10⁻⁸. The derived upper limit on ηR/X is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.